1. Field of the Invention
The present invention relates to a tape cassette, which is formed by a material of higher transparency in order to detect an end of a magnetic tape by detection light from a light source for detecting an end of tape inserted into a cassette half.
2. Description of the Related Art
FIG. 1 is a plan view of a conventional tape cassette according to the prior art.
FIG. 2 is a perspective view of the conventional tape cassette shown in FIG. 1.
FIG. 3 is a fragmentary cross-sectional view of the conventional tape cassette shown in FIG. 1 for explaining a light path between a light emitting element and a light receiving element inside the tape cassette.
FIG. 4 is a side elevation view in cross section of the conventional tape cassette for explaining the light path between the light emitting element and the light receiving element shown in FIG. 3.
FIG. 5 is a side view of the conventional tape cassette shown in FIG. 1.
FIG. 6 is a partially enlarged side view of the conventional tape cassette shown in FIG. 1.
FIG. 7 is a side elevation view partially enlarged in cross section of the conventional tape cassette for exhibiting a state of scattered light beam reaching to the light receiving element as an undesired light beam in the cassette half.
In FIGS. 1 through 7, a tape cassette AA is composed of an upper half 1, a lower half 2, a top lid 3, a front lid 4, a window 5, two upper flanges 6a and 6b, two lower flanges 7a and 7b, right and left holes 8a and 8b for light path, two hubs 9a and 9b, and a magnetic tape T. The upper half 1 is further composed of an outer right side 1A1, an outer left side 1B1, an inner right side 1A2, and an inner left side 1B2. The upper flange 6a is formed with a top surface 6a1 and a bottom surface 6a2 and the other upper flange 6b is formed with a top surface 6b1 and a bottom surface 6b2. Furthermore, in FIGS. 3, 4, and 7, “D1” is a light emitting element, each of “D2” and “D3” is a light receiving element, and each of “L1” and “L2” is a detection light beam detected by respective light receiving elements D2 and D3, wherein the detection light beams L1 and L2 are generically referred to a light path L. Moreover, in FIG. 1, symbols A and A′ represent neighboring areas of the right and left holes 8a and 8b respectively.
A tape end is detected by detecting a light beam irradiated from a light source for detecting a tape end by receiving more than a predetermined luminous energy of the light beam, wherein the light source is inserted into a tape cassette. The tape cassette AA having a configuration of detecting both ends of the long magnetic tape T, which is wound around the both hubs 9a and 9b with contacting along the upper and lower flanges 6a, 7a, 6b, and 7b, is organized so as to form the light path L such that a light beam irradiated from the light emitting element D1, which is mounted on a video tape recorder (hereinafter referred to a VTR), not shown, as a light source, reaches the light receiving elements D2 and D3.
Generally, in the tape cassette AA shown in FIGS. 1 and 2 being constructed by a material having high light shielding ability such as black, if there existed the magnetic tape T in the light path L as shown in FIGS. 3 and 4, the light beams L1 and L2 irradiated from the light emitting element D1 are shielded by the magnetic tape T. Accordingly, the light receiving elements D2 and D3 become an extremely low luminous energy receiving condition, that is, the light receiving elements D2 and D3 can hardly receive the light beams L1 and L2.
A leader tape section (not shown) not coated with magnetic powder is provided at both ends of the magnetic tape T rolled up inside the tape cassette AA. These leader tape sections are formed by a material being pervious to a light beam irradiated from the light emitting element D1.
Therefore, while the magnetic tape T is running after the tape cassette AA has been loaded into a VTR, luminous energy received by the light receiving elements D2 and D3 of the light beam irradiated from the light emitting element D1 changes rapidly from low to high as much as exceeding the predetermined luminous energy at a time when the magnetic tape T shifts from a magnetic tape section coated with magnetic powder over to the leader tape section. Accordingly, the end of the magnetic tape T can be detected.
In FIGS. 4 and 5, a roughening treatment is not applied on upper surfaces of the right and left holes 8a and 8b for the light path, which are provided by combining the upper and lower halves 1 and 2 with each other, that is, the outer right and left sides 1A1 and 1B1 are not roughened, although the upper half 1 is formed by a material of high transparency and the lower half 2 is formed by a black material without transparency.
An external light beam, which entered into the tape cassette AA through the upper half 1, passes through an inside of the tape cassette AA and gets out from the tape cassette AA through the upper half 1 once again. A part of the light beam getting out through the upper half 1 passes through the upper half 1 from the inner right and left sides 1A2 and 1B2 to the outer right and left sides 1A1 and 1B1. In a case that the external light beam passed through the upper surfaces of the right and left holes 8a and 8b, that is, through the upper half 1 from the inner right and left sides 1A2 and 1B2 to the outer right and left sides 1A1 and 1B1 gets into the light receiving elements D2 and D3, the light receiving elements D2 and D3 detect light reception if the luminous energy of the external light beam gotten into the light receiving elements D2 and D3 exceeds the predetermined luminous energy, even though the detection light beams L1 and L2 irradiated from the light emitting element D1 do not reach to the light receiving elements D2 and D3.
Thus, the VTR accidentally determines that the magnetic tape T has come to its end although the magnetic tape T is not in the terminal position of the tape. Accordingly, the VTR may stop functioning while the magnetic tape T is still running.
As mentioned above, in a case that at least the upper half 1 out of both upper and lower halves 1 and 2 constituting the tape cassette AA is formed by a material of high transparency or a semitransparent material, an external light beam such as sunlight may enter into the tape cassette AA through the upper half 1. The external light beam entered into the tape cassette AA reaches to the light detecting elements D2 and D3 provided on the VTR as transmission light or scattered light, that is, undesired light other than the detection light beams L1 and L2 through the upper surfaces of the right and left holes 8a and 8b, that is, through the upper half 1 from the inner right and left sides 1A2 and 1B2 to the outer right and left sides 1A1 and 1B1 even when the magnetic tape T is running in the VTR. The light detecting elements D2 and D3 detect light reception if luminous energy of the external light beam exceeds a detectable level of the light receiving elements D2 and D3. Thus, the VTR accidentally determines that the magnetic tape T has come to its end although the magnetic tape T is not in the terminal position of the tape. Accordingly, the VTR may stop functioning while the magnetic tape T is still running.
Further, the light emitting element D1 as the light source for detecting a terminal position of a tape always irradiates a light beam during a period of time until the tape cassette AA is ejected after the tape cassette AA has been loaded into the VTR. Furthermore, a light irradiating position of the light emitting element D1 is arranged at a predetermined angle with respect to allocations of the light receiving elements D2 and D3. Accordingly, a light beam irradiated from the light emitting element D1 is split into direct light, which directly reaches to the light receiving elements D2 and D3 through the right and left holes 8a and 8b for the light path, and scattered light, which reaches to the light receiving elements D2 and D3 through the upper half 1 in vicinities of the right and left holes 8a and 8b after the light beam irradiated from the light emitting element D1 has been scattered inside the tape cassette AA.
Then, the light receiving elements D2 and D3 detect light reception if the luminous energy of the scattered light exceeds the detectable level of the light receiving elements D2 and D3. Thus, the VTR accidentally determines that the magnetic tape T has come to its end although the magnetic tape T is not in the terminal position of the tape. Accordingly, the VTR may stop functioning while the magnetic tape T is still running.